XIII 



PHYLUM CHORDATA 



605 



the presence of a bony dermal carapace and a bony investment for 

 the tail ; but in the Glyptodontidae the carapace has no movable 

 rings, so that the animal could not roll itself up, and there is 



FIG. 1233. Mylodon robustus. (Restoration, after Owen). 



usually a ventral bony shield or plastron, never present in the 

 Armadillos. Glyptodonts occur in North as well as in South 

 America. The Megatheriidse (Fig. 1233) are Edentates, mostly 

 of enormous size and massive build, which combine certain of the 

 features now characteristic of the Anteaters (Myrmecophagidae) 

 and the Sloths (Bradypodidse) respectively, the spinal column and 

 limbs allying them with the former, and the crania and the teeth 

 with the latter. 



The Cetacea are represented in the Tertiary (Eocene and 

 Miocene) of Europe, Egypt, and North America, by an extinct 



FIG. 1234. Squalodon. Three of the lower true molars. (After Flower.) 



sub-order Archceoceti or Zeuglodonta, comprising only one 

 known genus Zeuglodon. Zeuglodon differs from existing Cetacea 

 mainly in the possession of rooted, heterodont teeth, and in the 

 VOL. ir p p 



